1. Field of the Invention
The invention relates to methods and systems for charactering movement of objects.
2. Discussion
Several techniques are known for determining a speed of a moving object: (a) Direct, active measurement, in which an electro-magnetic field, e.g, radio, infra-red, visible-light, or an acoustic field, e.g., ultrasonic, is directed generally at an object to be measured. Reflected energy is then analyzed to determine the speed of and/or the distance to the object. Examples of such systems implementing direct, active measurement include radar and lidar. (b) Mechanical measurement, in which an arrangement of detectors is placed such that a moving object triggers the detectors, and the time difference between the trigger events is used to calculate speed. The detectors may be, for example, beams of light or mechanical switches. (c) Focus analysis, in which an electronically-sensed image is analyzed for correct focus, that is, correct setting of the image-forming lens between the object and the image-sensing element. Such analysis, e.g., image contrast enhancement, parallax analysis, yields a distance to an object. Computing the change in focus-distance permits the computation of a component of speed of the object.